Tartilla,

I have no idea what the alternator is actually putting out. Like I said, I had it tested, while the engine was out, and it was over performing at the time. Don't remember the number. It's been a hot minute. What's the spec output of the OWM 496 alternator? I'll try and check it again this weekend.

I would agree that we are not drawing that much. But the overall feeling is that the alternator is barely keeping up. My main wonder is around the fact that we are now charging both batteries simultaneously, whereas before, it was only the one the battery selector switch was set to.

If memory serves, there's a 10A fuse on the power input wire going to the ECM, but there is also a fuse at the relay for the injectors.

It was suggested that I run the two blowers through a relay when I installed the second blower, and I elected to draw straight from the switch. I even bumped up the breaker to 10A (replacing a 5A). Maybe I need to address that over the winter, too.

The thru-transom exhaust sound is normal. The fuel pump whine is new, and, to be fair, it IS an annoying sound. And it's fairly prominent at idle. She said it can be heard as she's walking down the ramp after parking the truck.

Thanks. Brad.

Its not a free diagnosis.. but this is a good piece of kit to have on a boat anyways..

I believe the stock 496 alternator is 65A.
You can measure DC current with a clamp meter like this so you can get actual amperage output from your alternator..

One thing I'm wondering is if your checking your voltage levels at idle? Most alternators, except special built ones, are barely putting out anything at idle RPM. Most won't output full capacity until at least 2000 RPM, so unless you're checking voltage levels at higher rpms, it won't really be accurate unless you're rev'ed up a bit. But again, checking voltage levels isn't really telling you the full story.. You need to be able to measure current output to see if its actually keeping up with the charging needs.

You also mentioned you are using a battery isolator.. These are essentially diodes, which have a nominal voltage drop of 0.6 to 0.7 volts.. So the output of your battery isolator will never be higher than your alternator voltage output minus 0.6 volts.. So if you spend a lot of time idling around the lake, your isolator voltage will be too low to charge.. You should check the voltage at the input and output of the isolator and verify this voltage drop.

I think step one is to actually measure your alternator output voltage and current at 2000ish RPM.

Have you individually load tested both batteries? You could have bad cell(s) in a battery causing the issue. I've seen it before, even on a Optima Blue Top in my 37AT.

Sydwayz,

I have not. But one of them is brand new and they both meter about the same. It's certainly worth looking into.

Thanks. Brad.

AShipShow,

Thanks for the spec on the alternator. I was thinking 70A but didn't really know.

It's the idle speed output I'm most worried about. But, I'll admit, I don't recall actually looking at the volt gauge on the dash while running down the lake. I'll have to do that.

BlueSea Systems calls it an ACR; Automatic Charging Relay. It's just a switch. I don't believe it has diodes. I believe its default is open circuit, isolating the batteries whenever it sees a load (starting, radio, bad battery, etc) or no current, and closes when it sees a charge. It doesn't really have an "output". It is just a switched bridge between the two output lugs of the selector switch. I guess with this said, it would stand to reason that we are seeing a positive charge, over that of demand, or the ECM battery would be down significantly by the end of the day' Logic being, if there were no charge above demand, the ACR would open, and a charge would only go to the battery the selector switch was set on, which has been #2. Am I reasoning that out correctly?


There is a ground wire that has since been connected to the ACR that allows it to be an active circuit, detecting current.

Thanks. Brad.

We all know manufacturing QC has gone to shlt since Covid. I can attest as I had a brutal wreck in my racecar due to a simple failed brake component. And we've all at one time or another pulled a brand new broken product out of the box.

Ah, gotcha.. yea, ACRs have basically no voltage drop, so thats a way better system. It might not be working though, you should verify that the contacts are closing when the boat is running.. I believe it has to see over 13 volts for over 30 seconds or a minute or something to close and charge the battery..

Some good advise here, I am a dual engine but isolate and use dual blowers. You should not have low voltage issues, pretty much anything over 1200 rpm and I hover right around 14v. (13.8).

The bilge blower could be put on a relay, amazing how much that helps, I also did it with my hatch ram.

Check the current and voltage out right at the alternator first, then go from there. Who know you may have a bad connection on the main alternator feed. Sometimes even the crimp gets bad.


I use these relays in my little boat.

I used one but it has a switch that I can control the voltage it drops at, use it on my stereo. Nice units.

Lot of good info for ya here Brad. If you’re running 12.5 at idle with a load on your prob ok. Speaking from my PQ experience the dash wiring isn’t great. They run small insufficient gauge wire to the helm and daisy chain everything together. Two things I did that helped a lot; first - run a large power and ground up near helm, set up 2 buss bars and supply dash from there.
Second, power your hatch ram through relays at the rear and control the relays with your dash switch. Your hatch will run faster and won’t make strange things happen with dash while raising hatch.
You probably run at least 3000-3500 when cruising so if alt output is ok at 2000 your good to go.